Dissolved Rare Earth Elements Distribution in the Solomon Sea

Trace Elements and Isotopes (TEIs) were measured as part of the GEOTRACES PANDORA cruise (July-August 2012, R/V L'Atalante), among them Rare Earth Elements (REEs) as pertinent tracers of land-ocean inputs and water mass transformations. This work discusses results of 19 dissolved REE (dREE) profiles measured using a trispike method in the Coral Sea and inside and at the exits of the Solomon Sea, a semi-enclosed sea with complex topography and straits. Overall, dREEs -except the insoluble Ce- show nutrient like profiles, i.e. depleted at the surface and enriched at depth. Illustrative Nd concentrations range from similar to 5 pmol/kg at the surface to > 25 pmol/kg at 5000 m depth. However, local dREE enrichments are observed, mostly in the Straits (Indispensable, Solomon and Vitiaz Straits) and along the island coasts. A box model allows calculating and discussing the fate of the dREEs in the different water layers flowing through the Solomon Sea. Finally, subtle variations revealed by La, Ce, Eu anomalies and the normalized light versus heavy REE ratio (expressed as Nd-n/Yb-n) allows the identification of specific mechanisms affecting the distribution of the different dREEs. The positive Eu anomaly observed in the surface layers reflects the basaltic origin of external inputs, consistent with the intensive weathering and/or volcanic activity affecting the surrounding islands. These data also confirm that the distributions of heavy dREEs (like Yb) are better correlated to the dSi concentrations than that of the other REEs. This article is part of a special issue entitled: "Cycles of trace elements and isotopes in the ocean - GEOT-RACES and beyond" - edited by Tim M. Conway, Tristan Homer, Yves Plancherel, and Aridane G. Gonzalez.